In high luminance light sources often a phosphor is used as a converter being excited by blue light emitted by a laser. For measurement and control of the emitted light the converter head could be equipped with sensors or detectors. The feedback signals of the detector or sensors are used to control the laser. Eye-safety of such laser-based light sources has to be guaranteed even in case of a malfunction. Furthermore, the physical form factor of the laser based-light source should be flexible in order to increase freedom of design of, for example, a vehicle headlight comprising such laser based-light source.
US20090296018A1, DE102013207841A1, and DE102013207841A1 proposed various methods for monitoring the function of the converter as well as of a light guide used for transporting the excitation radiation to the converter. In particular, it was proposed to realize the light guide either as a bundle of optical fibers or as a structure of branched light paths where one fiber or light path then can be used for back guiding part of the converted light to a monitoring detector whereas the other fibers or light paths then serve for forward guiding the excitation radiation to the converter. Due to using several fibers or branching structures, unfortunately, these systems are complex and costly.